Interpretation of hysteresis measurements for perpendicular double-layer media

A method is given for the extraction, from VSM measurements, of saturation magnetization, coercivity, thickness, and squareness of perpendicularly oriented double-layer media. The CoCr coercivity in double-layer films is found to be less than that in similarly prepared single-layer films. The importance of coil balancing, sample centering, and sample alignment is discussed. For ideally square loops with demagnetizing factor 4π, all properties of each layer can be determined. The literature on CoCr, although conflicting, suggests these ideal conditions are not met. An independent measurement of thickness is required to determine the intrinsic squareness and demagnetizing factor. The degree of sensitivity of the results to these two parameters is derived.